1. Field of the Invention
The present invention relates to a method and apparatus for using DRM (Digital Rights Management) contents, and more particularly, to a method and apparatus for temporarily sharing DRM contents.
2. Description of the Related Art
Open Mobile Alliance (OMA) DRM defines a domain as a logical collection that shares one domain key. The domain key is generated by a server and is distributed to individual devices in a domain registration process. The devices that share the domain key receive a rights object (RO) that is encrypted by the domain key, such that terminals belonging to the domain can share contents. If a device is taken out of the domain, the domain key is updated, and this update is reported to all the devices. Then, the contents are redistributed.
A home domain has a domain manager that manages the domain and general DRM devices. In general, the domain manager serves as a master and the general devices serve as slave or guest devices. The domain manager searches the guest devices, performs authentication, and registers the domain key. The domain key is generated by the domain manager. Then, the domain is formed.
The domain has a server that involves in forming the domain, and a user selects devices to be registered in his/her domain among devices that present on the server. The server transfers a certificate revocation list downloaded from an external server to the devices selected by the user. The certificate revocation list includes information for identifying devices revoked by a broadcast encryption system.
Each of the devices creates a certificate for the public key using a secret value extracted from the certificate revocation list transferred from the server and transfers the certificate to the server. The server verifies the legitimacy of the devices through the certificate verification, and unique IDs and the public keys of the authenticated devices are stored in an authentication list. Further, the server generates a unique domain ID and a domain key using the unique IDs and the public keys of the devices in the authentication lists and a random number. At this time, the random number is generated by the server. Then, the domain key and the domain ID that are encrypted by the public keys of the individual devices are transferred to the devices in the authenticated domain.
To this end, the following procedure is taken.    1. The master device and the guest device to be used are turned on.    2. If the master device is turned on and is connected to a home domain network, the authentication is performed on whether or not the devices connected to the network are legal devices.    3. After the devices are authenticated, the user registers the devices in a list of the master in order to register the device in the home domain.    4. When a device is added or deleted, a new domain key is generated.    5. The registered guest devices are subject to a mode change as slave devices.    6. All the slave devices safely receive the new domain key.
According to this procedure, whenever a new device is added or deleted, this needs to be registered in the server, which causes overhead. Accordingly, it is impossible to freely share the contents.
FIG. 1 is a diagram showing an operation for generating and distributing a rights object on the contents that is provided in a related art OMA DRM architecture. Various devices D1, D2, D3, and D4 in the domain are registered as members of the domain through a registration procedure to a service provider. Then, the individual devices D1, D2, D3, and D4 can share the contents and the rights object with other devices.
Here, one representative device D1 can transmit the acquired contents and rights object to other devices D2, D3, and D4 so as to share the contents and the rights object with other devices. Then, the other devices can reliably use information of the received contents and rights object on the basis of information of the service provider.
A general DRM system transmits the contents encrypted by a contents provider or a rights issuer in order to protect the contents from illegal usage. In addition, in order to protect the use of the contents, a rights object including usage rules of the contents is issued so as to protect the rights of the original author. To this end, the DRM devices are designed to forcibly keep the usage rules included in the rights object.
In the OMA DRM architecture v2.0, rights information (that is, RO) of the contents is shared using the domain. The procedure is as shown in FIG. 1.
First, four devices exists in one domain, and, in a server-based domain technique, a contents server includes a root certificate and a service provider certificate for generating a rights object including encrypted contents, an encryption key for using the encrypted contents, and usage rules. The root certificate is a certificate of a certificate issuer for confirming an authenticating system, and the service provider certificate is a certificate for representing that the public key of the service provider is authenticated from the certificate issuer.
Referring to the flow of FIG. 1, the devices D1, D2, and D3 are registered to the rights issuer and join in the domain (1). The device D1 acquires the contents and rights object from the rights issuer (2), and transmits the acquired contents and rights object to the devices D2 and D3 (3). Meanwhile, even though the device D1 transmits the contents and the rights object to the device D4, as shown in (4), since the device D4 is not registered to the rights issuer yet, a process (5) of allowing the device D4 to be registered to the rights issuer and to join in the domain is required.
Accordingly, there is a need for a method and an apparatus that enable the rights object to be freely used among the devices belonging to the same domain, thereby enabling the usage of the contents with no interruption.